Just take ure receipt or a form of visit visa filled and go to jawazat of madina khalifa gate 1 first floor between 6 am and 11 am, going early is better, there u will find captain ( NASSER AL ATTIYA) and many people will b there for same prblm just explain ure situation for him he may sign for u the form for ure mom to come again before she complet 3 months outside qatar .. wish u all the best.